A user with admin privileges is sometimes called a <em>super user</em>. This is simply because that user has more privileges than normal users. You might see people discussing things like <cmd>su</cmd> and <cmd>sudo</cmd>; these are programs for temporarily giving you "super user" (admin) privileges.

If you had admin privileges all of the time, you might accidentally change an important file, or run an application which changes something important by mistake. Only getting admin privileges temporarily, when you need them, reduces the risk of these mistakes happening.